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any distortion of the enone from planarity would be expected to decrease the reactivity through loss of conjugation.Our results, in conjunction with Helmchen's work (vide supra), provide strong evidence that the reactive geometry of TiCl4-enone complexes may be of an out-of-plane type; further work will be required to establish whether this is a general phenomenon. These results do not, of course, imply that a preference for an out-of-plane reactive geometry exists for other Lewis acids; TiCl4 may be unique in this regard. However, our results do point out the need for caution in basing predictions of reactive geometries on X-ray and spectroscopic data.Acknowledgment. Financial support by the National Science Foundation (CHEM-8813618) and by the donors of the Petroleum Research Fund, administered by the American Chemical Society, is gratefully acknowledged. Supplementary Material Available: Details of the synthesis and characterization of compounds 1-5 as well as the kinetics procedures (13 pages). Ordering information is given on any current masthead page.(26)NMR competition experiments employing 1/1/1 la/le/TiCl4 and 2a/2e/TiC!4 Indicated a 14/86 ratio of la-TiCl4/le-TiCl4, but that 2a does not effectively compete with 2e for TiCl4 (only 2e-TiCl4 present). We thank a referee for suggesting this experiment.

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